A man sells a book at a profit of 20% . If he had bought it at 20% less and sold it for Rs. 18 less, he would have gained 25% . The cost price of the book is = ?

Solution(By Examveda Team)

Let the C.P. be Rs. 100
Then,
Profit = 20%
S.P. = Rs. 120
New C.P. = 20% less = Rs. 80
If he gain is 25% then S.P.
$$\eqalign{ & = {\text{Rs}}\left( {\frac{{125}}{{100}} \times 80} \right) \cr & = {\text{Rs}}.100 \cr} $$
Difference in S.P.
= Rs. (120 - 100)
=Rs. 20
If difference in S.P. is Rs. 20, then C.P. = Rs. 100
If difference in S.P. is Rs. 18, then
$$\eqalign{ & {\text{C}}{\text{.P}}{\text{.}} = {\text{Rs}}.\left( {\frac{{100}}{{20}} \times 18} \right) \cr & \,\,\,\,\,\,\,\,\,\,\,\, = {\text{Rs}}{\text{. }}90 \cr} $$